In the use of hydraulic excavator equipment, unless the center line of the excavation lies in a vertical plane passing through the longitudinal axis of the excavator, the side or lateral walls of the excavation are not maintained normal or perpendicular to the work plane upon which the excavator is operating. However, in many instances it is desirable or necessary to excavate from a position wherein the excavating or digging arm is operating in a position offset laterally from the longitudinal axis of the excavator. In order to maintain the side walls of the excavation perpendicular or normal to the ground surface work plane it has been necessary to tilt the excavator or the excavating arm about the longitudinal axis of the excavator.
Such tilting is necessary because as the lifting arm, to which a digging bucket is operatively connected, is raised or lowered in digging operations, the relative position between the bucket and the longitudinal axis of the excavator base is changed. The movement of the lifting arm, when excavating laterally of the excavator base, causes the plane of bucket movement to be rotated about the longitudinal axis of the excavator resulting in a "tilted" trench, both as to the excavation side walls and bottom.
As a consequence of the moving of the lifting arm, this rotation of the path of bucket movement with respect to the longitudinal axis of the excavator base effects a different tilt to the side walls of the excavation. The side walls so formed do not lie in parallel planes normal to the excavator base and work plane, with the degree of tilt being proportionately greater as the depth of the excavation increases. Such asymmetry in the excavation side walls requires further finishing work to eliminate this tilt of the side walls as well as the slope of the excavation bottom.